Multiple sources close to the situation said that the online search and advertising deal between Microsoft and Yahoo has been struck and will be announced within the next 24 hours.

While it is not clear if the actual papers have been inked or approved by the board of the two companies, sources said it was a formality and that negotiations are complete on a deal that is less sweeping than originally conceived.

In any case, making any partnership is likely to be the cause of much relief at both companies, since they have been trying–without success–to join together to mount a better offense in the sector against the dominant Google (GOOG).

According to sources, as had been previous reported by Advertising Age, there will be no upfront payment to Yahoo, with the focus on a revenue share between the two companies.

Sources said Microsoft search technology will be used on Yahoo sites, although it is not clear if it will be branded as “powered by Bing”–Microsoft’s handsome new search offering–or not.

In addition, sources said Yahoo would still sell search ads on its sit